Is the demand for certainty satisfied where, after a survey of relevant, state-law materials, the federal court can only say what is "suggestive" and what "appears" from those materials, and where the federal court then looks to policy reasons identified by this Court in interpreting a federal statute as an indication of how the state statute should be read?

Is the demand for certainty satisfied where, after a survey of relevant, state-law materials, the federal court can only say what is 'suggestive' and what 'appears' from those materials, and where the federal court then looks to policy reasons identified by this Court in interpreting a federal statute as an indication of how the state statute should be read?